The discovery of strong luminescence at room temperature from silicon cluster has attracted an enormous attention in recent years due to its potential applications in Si-based optoelectronic devices, especially blue and UV luminescence devices. Several studies have addressed the question of augmentation and stabilization of luminescence emission with different treatments, such as electron irradiation, thermal treatments and ion implantations. Even though observed visible light can be explained by the quantum confinement (QC) effect, many experimental results obey to the QC model supported surface state. Theoretically, the effects of quantum confinement on band gap of silicon indicate that it should be possible to obtain a blue light or shorter wavelength photons from the porous silicon if the silicon crystal size can be reduced to a certain value, e.g. to the diameter of 2-5 nm. However, it is rather difficult in practice to obtain a blue/white luminescence even when nanocrystals with diameters smaller than 2.0 nm are present. Some authors attributed this difficulty to the formation of surface Si–O bonds, which lead to mid-band gap trapped electrons and hole exciton states and thereby remove the dependency of the luminescence on cluster size. But in this case a luminescence emission was obtained in the red and yellow regions. It was found that some post-treatments such as anodic oxidation and oxidation in air could reduce the effective size of the Si nanocrystallites, thus causing a blue shift of the luminescence spectrum. If the red-yellow emission of the PS could be combined with a blue/green emission by modification of the PS surface such as oxidation or metal coating, it would be possible to obtain white light. This would mean an economical route to silicon based LEDs. Silicon dioxide, SiO2, is widely distributed in the environment, and is present in the form of sand on all beaches and deserts. It is the starting material for the production of silicate glasses and ceramics. It may occur in crystalline or amorphous form, and is found naturally in impure forms such as sandstone, silica sand or quartz. Its specific gravity and melting point depend on the crystalline structure. Silica is known to occur in many crystalline phases or modes (┙-quartz, ┚-quartz, ┙-cristobalite, ┚-cristobalite, ┙-tridymite, ┚tridymite, ┛-tridymite, coesite, melanophlogopite, keatite, fasriges, stishovite, chalcedon, agate, moganite, and others) besides some amorphous phases (opal, hyalite, sintered pearl, lechateierite, natural silica glass) [Fanderlik 1991]. Silicon dioxide is not only one of the most abundant materials on earth as mentioned, but also a critical material component of considerable technological importance. Today's modern electronics greatly depends on silicon dioxide for the manufacture of semiconductors and microelectronic devices, besides

/pdf/defect-related-luminescence-in-silicon-dioxide-network-a-kfewor1yv6.pdf

Defect Related Luminescence in Silicon Dioxide Network: A Review

Motivated by the necessity to have all silicon optoelectronic circuits, researchers around the world are working with light emitting silicon materials. Such materials are silicon dielectric compounds with silicon content altered, such as silicon oxide or nitride, enriched in different ways with Silicon. Silicon Rich Oxide or silicon dioxide enriched with silicon, and silicon rich nitride are without a doubt the most promising materials to reach this goal. Even though they are subjected to countless studies, the light emission phenomenon has not been completely clarified. So, a review of different proposals presented to understand the light emission phenomenon including emissions related to nanocrystals and to point defects in SiO2 is presented.

/pdf/emission-mechanisms-of-si-nanocrystals-and-defects-in-sio-2-42ivu006ts.pdf

Emission mechanisms of Si nanocrystals and defects in SiO 2 materials

In this paper we describe the implementation of a fuzzyrelational neural network model. In the model, the input features are represented by their respective fuzzy membership values to linguistic properties. The weights of the connections between input and output nodes are described in terms of their fuzzy relations. The output values during training are obtained with the max-min composition, and are given in terms of fuzzy class membership values. The learning algorithm used is a modified version of the back-propagation algorithm. The system is tested on an infant cry classification problem, in which the objective is to identify pathologies like deafness and asphyxia in recently born babies. The design and implementation of the classifier is presented, as well as results of some experiments.

Implementation of a Linguistic Fuzzy Relational Neural Network for Detecting Pathologies by Infant Cry Recognition

Silicon rich oxide (SRO) films have various applications as optoelectronic devices, especially as light emitters. Nowadays, the emission mechanisms in the SRO films are not completely understood, leading to a high potential field of research. The study of the SRO film's characteristics and its relation with the absorption and emission spectra would provide information on the mechanism of radiation. Moreover, the optical and electrical characteristics of the SRO films need to be understood in order to improve and propose novel devices. In this work the study of the optical and electrical properties of the SRO films is done. Photoluminescence, absorption spectra, AFM, refractive index and I – V characteristics in the SRO films were obtained and analyzed. The silicon excess and defects in the SRO films should have an important role in the photocurrent. We assume that a high responsivity to a visible light of the SRO/Si junction is achieved probably due to a combined effect of electron hole pairs in the silicon substrate and photo excited electrons in the SRO films.

Optical and electrical properties of silicon rich oxide films for optical sensors

In the present work, non-stoichiometric silicon oxide films (SiOx) deposited using a hot filament chemical vapor deposition technique at short time and simple parameters of depositions are reported. This is motivated by the numerous potential applications of SiOx films in areas such as optoelectronics. SiOx films were characterized with different spectroscopic techniques. The deposited films have interesting characteristics such as the presence of silicon nanoclusters without applying thermal annealing, in addition to a strong photoluminescence after applying thermal annealing in the vicinity of 1.5 eV, which may be attributed to the presence of small, oxidized silicon grains (less than 2 nm) or silicon nanocrystals (Si-nc). An interesting correlation was found between oxygen content, the presence of hydrogen, and the formation of defects in the material, with parameters such as the band gap and the Urbach energies. This correlation is interesting in the development of band gap engineering for this material for applications in photonic devices.

Spectroscopic Properties of Si-nc in SiOx Films Using HFCVD.

The off-stoichiometry silicon oxide SiOx (x < 2), known as silicon-rich oxide (SRO), and silicon-implanted thermal silicon oxide (SITO) have shown poor photoluminescence (PL) at room temperature. Recently, many efforts to increase the PL in these materials have been made. In our experiments, a considerable increase of the visible emission has been observed when the SRO is super-enriched by silicon implantation. In this experiment, SITO and LPCVD-SRO with different silicon excess, Si implanted and no implant were studied. Different doses of silicon, and annealing in N2 at different temperature and times were used. PL response was measured before and after annealing. The emission is explained as the decay between traps in the oxide gap. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Silicon excess and thermal annealing effects on the photoluminescence of SiO2 and silicon rich oxide super enriched with siliscon implantation

The photoluminescence properties of silicon rich oxide (SRO) and silicon oxynitride (SNO) films were studied. The materials were obtained by the low pressure chemical vapor deposition (LPCVD) technique, with some samples post- treated by Si-implantation and thermal annealing under different conditions. For SRO films, strong red emission with peak at 1.7 eV was observed after Si-implantation and thermal annealing. The emission intensity depends on the deposition and post-treatment parameters. For SNO films, however, strong blue emission with a peak at 2.38-2.66 eV was observed both in the as-deposited and annealed states. The emission intensity and peak position can be adjusted by thermal annealing. This emission band was also compared with that produced by PECVD-SRO films. The experimental results were explained according to the structural properties of each material. It could be possible that the emission depends not only on Si excess but also on the microstructure of the material.

Photoluminescence in off-stoichiometric silicon oxide compounds

Photoluminescence (PL) properties of thin and thick silicon-rich oxide (SRO) and silicon implanted SRO (SI-SRO) films with different silicon excess fabricated by low pressure chemical vapor deposition (LPCVD) were studied. The effects of the annealing temperature and silicon implantation on the PL were also studied. Maximum luminescence intensity was observed with an annealing temperature of 1150 and 1100 ◦ C for thin and thick SRO films, respectively. The PL intensity is strongly enhanced when SRO films are implanted with silicon, especially for thin SRO films. Thin SI-SRO films emit up to six times more than non-implanted films, meanwhile the PL in thick SI-SRO films is only improved less than two times. Therefore, thin SI-SRO films are an interesting alternative for applications such as the fabrication of efficient Si-nps based LEDs.

Materials Science and Engineering B

This paper presents the cointegration of an UV silicon sensor with extended responsivity, and its conditioning circuit. The sensor's output current is converted to a digital code for subsequent processing. Post-layout results shows a suitable response in order to obtain a digital code corresponding to sensor photocurrent in the range of 200 to 1100nm. The circuit has been designed in a CNM 2.5µm CMOS technology.

Design of a CMOS transducer interface for an UV silicon sensor

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Papers

Silicon excess and thermal annealing effects on the photoluminescence of SiO2 and silicon rich oxide super enriched with siliscon implantation

Photoluminescence in off-stoichiometric silicon oxide compounds

Materials Science and Engineering B

Design of a CMOS transducer interface for an UV silicon sensor